Co-Assembled Supramolecular Organohydrogels of Amphiphilic Zwitterion and Polyoxometalate with Controlled Microstructures.

The organization of modifiable and functional building components into various superstructures is of great interest due to their broad applications. Supramolecular self-assembly, based on rationally designed building blocks and appropriately utilized driving forces, is a promising and widely used strategy for constructing superstructures with well-defined nanostructures and diverse morphologies across multiple length scales. In this study, two homogeneous organohydrogels with distinct appearances were constructed by simply mixing polyoxometalate (phosphomolybdic acid, HPMo) and a double-tailed zwitterionic quaternary ammonium amphiphile in a binary solvent of water and dimethyl sulfoxide (DMSO). The delicate balance between electrostatic attraction and repulsion of anionic HPMo clusters and zwitterionic structures drove them to co-assemble into homogeneous organohydrogels with diverse microstructures. Notably, the morphologies of the organohydrogels, including unilamellar vesicles, onion-like vesicles, and spherical aggregates, can be controlled by adjusting the ionic interactions between the zwitterionic amphiphiles and phosphomolybdic acid clusters. Furthermore, we observed an organohydrogel fabricated with densely stacked onion-like structures (multilamellar vesicles) consisting of more than a dozen layers at certain proportions. Additionally, the relationships between the self-assembled architectures and the intermolecular interactions among the polyoxometalate, zwitterionic amphiphile, and solvent molecules were elucidated. This study offers valuable insights into the mechanisms of polyoxometalate-zwitterionic amphiphile co-assembly, which are essential for the development of materials with specific structures and emerging functionalities.

Pharmacokinetics and Pharmacodynamics of Extended Infusion Versus Short Infusion Piperacillin-Tazobactam in Critically Ill Patients Undergoing CRRT.

BACKGROUND AND OBJECTIVES: Infection is the most common cause of death in severe AKI, but many patients receiving continuous RRT do not reach target antibiotic concentrations in plasma. Extended infusion of ß-lactams is associated with improved target attainment in critically ill patients; thus, we hypothesized that extended infusion piperacillin-tazobactam would improve piperacillin target attainment compared with short infusion in patients receiving continuous RRT. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: We conducted an institutional review board-approved observational cohort study of piperacillin-tazobactam pharmacokinetics and pharmacodynamics in critically ill patients receiving continuous venovenous hemodialysis and hemodiafiltration at three tertiary care hospitals between 2007 and 2015. Antibiotic concentrations in blood and/or dialysate samples were measured by liquid chromatography, and one- and two-compartment pharmacokinetic models were fitted to the data using nonlinear mixed effects regression. Target attainment for piperacillin was defined as achieving four times the minimum inhibitory concentration of 16 µg/ml for >50% of the dosing cycle. The probabilities of target attainment for a range of doses, frequencies, and infusion durations were estimated using a Monte Carlo simulation method. Target attainment was also examined as a function of patient weight and continuous RRT effluent rate. RESULTS: Sixty-eight participants had data for analysis. Regardless of infusion duration, 6 g/d piperacillin was associated with ≤45% target attainment, whereas 12 g/d was associated with ≥95% target attainment. For 8 and 9 g/d, target attainment ranged between 68% and 85%. The probability of target attainment was lower at higher effluent rates and patient weights. For all doses, frequencies, patient weights, and continuous RRT effluent rates, extended infusion was associated with higher probability of target attainment compared with short infusion. CONCLUSIONS: Extended infusions of piperacillin-tazobactam are associated with greater probability of target attainment in patients receiving continuous RRT.

Pharmacokinetics and pharmacodynamics of piperacillin-tazobactam in 42 patients treated with concomitant CRRT.

BACKGROUND AND OBJECTIVES: Current recommendations for piperacillin-tazobactam dosing in patients receiving continuous renal replacement therapy originate from studies with relatively few patients and lower continuous renal replacement therapy doses than commonly used today. This study measured the pharmacokinetic and pharmacodynamic characteristics of piperacillin-tazobactam in patients treated with continuous renal replacement therapy using contemporary equipment and prescriptions. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: A multicenter prospective observational study in the intensive care units of two academic medical centers was performed, enrolling patients with AKI or ESRD receiving piperacillin-tazobactam while being treated with continuous renal replacement therapy. Pregnant women, children, and patients with end stage liver disease were excluded from enrollment. Plasma and continuous renal replacement therapy effluent samples were analyzed for piperacillin and tazobactam levels using HPLC. Pharmacokinetic and pharmacodynamic parameters were calculated using standard equations. Multivariate analyses were used to examine the association of patient and continuous renal replacement therapy characteristics with piperacillin pharmacokinetic parameters. RESULTS: Forty-two of fifty-five subjects enrolled had complete sampling. Volume of distribution (median=0.38 L/kg, intraquartile range=0.20 L/kg) and elimination rate constants (median=0.104 h(-1), intraquartile range=0.052 h(-1)) were highly variable, and clinical parameters could explain only a small fraction of the large variability in pharmacokinetic parameters. Probability of target attainment for piperacillin was 83% for total drug but only 77% when the unbound fraction was considered. CONCLUSIONS: There is significant patient to patient variability in pharmacokinetic/pharmacodynamic parameters in patients receiving continuous renal replacement therapy. Many patients did not achieve pharmacodynamic targets, suggesting that therapeutic drug monitoring might optimize therapy.

BK-{beta}1 subunit: immunolocalization in the mammalian connecting tubule and its role in the kaliuretic response to volume expansion.

Large, Ca(2+)-activated K(+) channels (BK), comprised of alpha- and beta-subunits, mediate K(+) secretion during high flow rates in distal nephron segments. Because the BK-beta1 subunit enhances Ca(2+) sensitivity of BK in a variety of cells, we determined its role in flow-induced K(+) secretion and its localization in the mammalian nephron. To determine the role of BK-beta1 in the kaliuretic response to volume expansion, the rate of K(+) excretion (U(K)V) vs. varied urinary flow rates were determined in wild-type and BK-beta1 knockout mice (BK-beta1(-/-)). When flow rate was varied by volume expansion (2 ml.h(-1).25 g body wt(-1)) for 30 to 60 min in wild-type mice, we found that the U(K)V increased significantly with increasing urine flow rates (r(2) = 0.50, P < 0.00001, n = 31), as demonstrated previously in distal nephron of rats and rabbits. However, in BK-beta1(-/-) mice, U(K)V did not vary with changing flow rates (r(2) = 0.15, P = 0.08, n = 20). Using immunohistochemical techniques, we found that BK-beta1 was strongly expressed in the apical membrane of the murine distal nephron and that 98% of BK-beta1 protein detected by histochemistry colocalized with NCX, a marker of connecting tubules (CNT). Both BK-beta1 and NCX colocalized with BK-alpha in separate experiments. Furthermore, we confirmed BK-beta1 protein expression in the apical membrane of connecting tubules in rabbits. BK-beta1 RNA from rabbit CNT was sequenced and was identical to previously published rabbit muscle sequences. These data show that the BK-beta1 accessory subunit is present in the CNT segment of the mammalian distal nephron and has a significant role in the kaliuretic response to increased urinary flow induced by volume expansion.

TRPC4 forms store-operated Ca2+ channels in mouse mesangial cells.

Studies were performed to identify the molecular component responsible for store-operated Ca(2+) entry in murine mesangial cells (MMC). Because the canonical transient receptor potential (TRPC) family of proteins was previously shown to comprise Ca(2+)-selective and -nonselective cation channels in a variety of cells, we screened TRPC1-TRPC7 with the use of molecular methods and the fura 2 method to determine their participation as components of the mesangial store-operated Ca(2+) (SOC) channel. Using TRPC-specific primers and RT-PCR, we found that cultured MMC contained mRNA for TRPC1 and TRPC4 but not for TRPC2, TRPC3, TRPC5, TRPC6, and TRPC7. Immunocytochemical staining of MMC revealed predominantly cytoplasmic expression of TRPC1 and plasmalemmal expression of TRPC4. The role of TRPC4 in SOC was determined with TRPC4 antisense and fura 2 ratiometric measurements of intracellular Ca(2+) concentration ([Ca(2+)](i)). SOC was measured as the increase in [Ca(2+)](i) after extracellular Ca(2+) was increased from <10 nM to 1 mM in the continued presence of thapsigargin. We found that TRPC4 antisense, which reduced plasmalemmal expression of TRPC4, inhibited SOC by 83%. Incubation with scrambled TRPC4 oligonucleotides did not affect SOC. Immunohistochemical staining identified expressed TRPC4 in the glomeruli of mouse renal sections. The results of RT-PCR performed to distinguish between TRPC4-alpha and TRPC4-beta were consistent with expression of both isoforms in brain but with only TRPC4-alpha expression in MMC. These studies show that TRPC4-alpha may form the homotetrameric SOC in mouse mesangial cells.

Renal fluid and electrolyte handling in BKCa-beta1-/- mice.

Large-conductance Ca(2+)-activated K(+) channels (BK(Ca)) are composed of pore-forming alpha-subunits and one of four accessory beta-subunits. The beta1-subunit, found predominantly in smooth muscle, modulates the Ca(2+) sensitivity and pharmacological properties of BK(Ca). BK(Ca)-beta1 null mice (Mbeta1(-/-)) are moderately hypertensive, consistent with the role of BK(Ca) in modulating intrinsic vascular tone. Because BK(Ca) are present in various renal cells including the mesangium and cortical collecting ducts, we determined whether fluid or electrolyte excretion was impaired in Mbeta1(-/-) under euvolemic, volume-expanded, or high-salt diet conditions. Under euvolemic conditions, no differences in renal function were found between Mbeta1(-/-) and Mbeta1(+/+). However, glomerular filtration rate (GFR) and fractional K(+) excretion were significantly impaired in Mbeta1(-/-) in response to acute volume expansion. In contrast, Mbeta1(-/-) exhibited enhanced Na(+) excretion and fractional Na(+) excretion responses to acute volume expansion. Differences in renal function between Mbeta1(+/+) and Mbeta1(-/-) were not observed when chronically treated with a high-salt diet. These observations indicate that the beta1-subunit of BK(Ca) contributes to the increased GFR that accompanies an acute salt and volume load and raises the possibility that it is also involved in regulating K(+) excretion under these conditions.